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Extreme Planetary Features vs realism

Hello , I wanted to know if there is a discussion , a topic , a thread , a subforum where can be posed questions , or informations about extreme planetary features and their possible realistic believability on a fantasy planet .

For example ....

It wopuld be interesting to have a collection of informations of features and what would those cause to the planet , if allow life , how would change a planet etc ....

Some could be to a Planet ....

without moon ...

what happens if our planet had no moon ? No sea rises, no stabilization of the Axis tilting that would extremely change with seasons go up and down even to the equator ?

with two or more moon ...

what happens if our planet had more than one moon ? how would change sea rises, stabilization of the Axis tilting?

with a large igneous province

Just like the Siberian traps or others , would be possible to have anything like that and that life keeps going in the rest of the planet ? what
would change?

woth Larger than Earth or Smaller than Earth size

How would change gravity ? would be possible somehow to have the same Earthlike gravity?

With No tectonics

Like Mars , woul dhave no orography , no mountains? what woudl happen? to Magnetic field perhaps?

How does the climate change according to geographical features or Planetary formation? How would be a planet with all deserts and no plants, could be produced oxigen the same how woudl change life etc? Or if was mostly Icey ?

Those are just some of the possible questions on the Planet features and how could influence not only the shape, the formations of mountains, the oceans etc but also how woudl life react , if could survive , what could be the conditions to make the civilization still be possible to survive etc etc ?

IS there a section like that or would it be need to be created and if so Is it a good idea to have a place where to ask those questions?

How would change gravity ? would be possible somehow to have the same Earthlike gravity?

If the planet's density is the same as Earth's, then larger size results in stronger gravity on surface, and smaller size in weaker gravity on surface. It is possible for the surface gravity for a different sized planet to be comparable to that of Earth if it's composed from more/less dense material, although this is only feasible to some limit.

Originally Posted by Naima

With No tectonics

Like Mars , woul dhave no orography , no mountains? what woudl happen? to Magnetic field perhaps?

Mars does have mountains. It's largest mountain is much bigger than Mt. Everest.

I saw a couple of topics here and there but no specific thread about this.

I can risk answering some of your questions:

1- that is the main argument we hear about it. Haven't done any particular research on this topic I still know that even with the Moon, the Earth axial tilt is not 100% stable and can be influence a little by powerful earthquakes for example. And a faster rotating Earth with no Moon to slow it down could mean a different weather pattern if it's spin fast enough. as stipulated in the Geoff cookbook :The Climate Cookbook

2 - with two or more moon ... : It depend on the size on the moons especially the closest to the planet. The other are much less important. To avoid having them colliding with each others, multiple moons need to have some distance between them. The bigger they are, the bigger the distance required. Larger objects are harder to keep in orbit, so they can't be too far. The farther you move away from the planet, the weaker is it's gravity pull. At that point, the gravity pull of the star become stronger and it becomes a planet or dwarf planet possible with an unstable orbit since it's so close to a much bigger planet and it's moon(s).

So, with an earth-like planet, the possibilities are rather limited. You can add moons but they will be (usually) much smaller than OUR MOON. You could also make or moon close to make more space for others, or make it bigger. This will have a major impact as it will slow down the planet's rotation.

3- with a large igneous province
I don't know how this is affecting the climate considering that Siberia's climate is already harsh.

4- Gravity depend on the mass and not the size. It's possible the have a bigger and less dense planet but it can't be stretched very far otherwise the planet could collapse. Having more water is an easy way to achieve this.
A smaller planet with same gravity is also possible.

5: no tectonic activity : and a cold heart in the center of the planet mean no movements on the surface. I didn't know Mars had no tectonic activity. I though there was a huge volcano on it's surface named mount Olympus...

No tectonic activity means no more earthquakes and no more mountains formation. With enough time the center of the planet will cool down completely. Normally, for a planet the size of earth, it would take billions of years to achieve that. The Sun would be gone for long or changed in a white dwarf. Either options mean no more life Earth. The final days of the Sun will turn the Earth into a blazing desert, then, into a cold place like Mars or even colder. Maybe it's not the end of life but it's definitely the end of civilization.

The magnetic field would still be there but would be much weaker. But since we have a dying star, we don't need it as much.

The other scenario is highly improbable and question the existence of the Big Bang but : An old planet (or just a very large rock) formed around a star but the star eventually died. Time passes and from the remnants of the old star come a new one, much smaller but more welcoming for life. The planet is not in the habitable zone of the star but is still a dead rock. Now, from here, in this improbable scenario, is it possible for life to settle on that planet? I have no ideas. and it seems too far from the question anyway.

Hehe ok thankyou , but my thread is oriended toward the creation of a possible section where to discuss those topics so to have them organized and collected for future references.
So planetary building concepts that go beyond normal earthlike realities.

No moon -
While the moon probably stabilizes the movement of the Earth's axis somewhat, it's not at all clear how essential that is to life. Different authorities make different guesses, so take your pick.

There is some thought that tides (and particularly tidal zones) were critical in allowing life to make the transition to living on land. While that's probably true, lunar tides are not the only tides. The sun also causes tides which, though not as large as the lunar tides, would probably be enough to do the trick

Multiple moons -
Most moons in our solar system are nowhere near as large, relative to their planet, as the Moon is to Earth. Our moon is thought to be a statistical outlier, an accident of the later period of planet formation. The theory, which is supported by good evidence, has it that a Mars-sized proto-planet slammed into the proto-Earth late in formation, blasting a spray of debris out of the Earth's crust. Some of that debris was lost to interplanetary space, some fell back to Earth, and some formed the Moon.

This means that an Earth-sized planet is unlikely to have two large moons like our moon. Other worlds in our solar system have large moons, notably Pluto, so the odds of finding one around another Earth are not impossible, but I would not expect it to be common. Smaller moons, like Mars's two captured asteroids, might be common, and multiples of small moons might be common. We have not data yet with which to make an estimate.

If your world has multiple moons, they will interact with each other. For long-term stability (geologic timescales), the moons will have well-separated orbits not in harmonic resonance with each other. If your moons are similarly sized, they will appear as different sizes from the surface of your planet because of different orbital distances.

Of course, in a fantasy world with magic and so forth, you can have as many moons as you like, as large as you like.

Large igneous province - by which I assume you mean a region of active volcanism
Volcanoes affect climate in two ways. They put a lot of gasses into the air and they put a lot of particulates into the air. The gasses - methane, carbon dioxide, sulfur dioxide, and the like - are all strong greenhouse gasses. They enhance the atmosphere's retention of heat. The particulates, in the form of volcanic ash, act in much the same way as clouds do. By reflecting a portion of the sun's energy back to space, they reduce the amount of heat available to be captured at the Earth's surface and thus have a cooling effect. The particulates can be injected into the upper atmosphere and remain there for years.

On the whole, the balance is probably tilted toward cooling. The year after Penetubo (sp?) erupted was a cold and wet one for much of the northern hemisphere. The year after Krakatoa erupted was known as the year with not summer, with snowfall recorded in the summer in many paces int he United States. A prolonged period of eruptions by multiple volcanoes may allow greenhouse gasses to build up to a greater extent than these isolated eruptions did, but the amount of particulates would be correspondingly greater as well.

Life has survived periods of volcanism before, and probably would again. Life is marvelously adaptable. It's not clear that the thing we call civilization would be as adaptable, dependent as it is on a small number of intensely grown crops, but assuming people survived (which seems likely), some kind of civilization would be established in the new world.

Different size of planet -
A planet's gravity at the surface is dependent on the planet's radius and its mass: gravity = mass / square(radius). It's mass is a function of its mean density and its radius: mass = 4/3 pi x density x cube(radius). If you put those two together you see that gravity is proportional to density x radius. If you hold the density constant, then the gravity is proportional to the radius. The bigger the planet, the higher the gravity.

In the solar system, density is not constant. Even if you build the planets out of the same initial ingredients, they will be more compressed in a larger planet and we would expect larger planets, in general, to have higher densities. This is not always true. Mercury, in spite of being a very small planet, has a density almost as great as Earth's. And once a planet is large enough to retain hydrogen and helium in significant amounts, it's becoming a gas giant and its bulk density plummets.

The primary determinant of density may be the region of the solar system where the planet was formed. In our solar system, it is thought the planets were formed more-or-less in the orbits they inhabit today. There is evidence that Neptune has migrated into a wider orbit over time and that harmonic interactions between planets have adjusted other orbits somewhat, but that doesn't affect this argument much. The idea is that the inner planets formed in a region that was much hotter than the region the outer planets formed in. Heat is a measure of how fast molecules are moving. Hotter molecules are moving faster than colder ones and are harder to capture in a gravitational field. Bigger molecules move more slowly than smaller ones at a given temperature and are easier to catch. For this reason, the inner planets are systematically impoverished of the lighter elements, which means their densities are correspondingly higher. In the outer regions of the solar system, water ice behaves much as rock does in the inner system, and the low densities of many of the moons of the outer planets is a reflection of this.

What else would be different about different sized planets? A larger planet, with its higher gravity, would likely have smaller mountains. Mountains are limited by plastic deformation. If you pile stone high enough, it crushes or squishes and can no longer support the weight of the stone above it. It's no accident that the tallest mountain in the inner solar system is on Mars - it has a much lower gravity than does Earth.

The atmosphere might be different too. If the planet is too small, it can't retain an atmosphere. The Moon has a negligible atmosphere and Mars's atmosphere is 1%-2% the pressure of Earth's. A bigger planet, with higher gravity, can hang on to those lighter molecules longer. A planet larger than Earth might well have a thicker atmosphere, which would retain more heat than does Earth.

Venus is about the same size as Earth and has an atmosphere sixty times thicker. What gives there? One theory is that all the inner planets were originally burdened with the same heavy atmospheres composed primarily of carbon dioxide and methane and water. The gravity of Mars was too low to retain the atmosphere, and over a billion or two years the atmosphere of Mars bled off into space. On Earth, chemical reactions involving water and, later, the chemistry of life sequestered much of the carbon from the original atmosphere into the crust. Venus was enough hotter than earth that its water was photodisected and the hydrogen bled off into space. With no water, there was no mechanism to sequester the carbon, and Venus today is a balmy 750 Kelvins.

Earth is, according to many estimates, on the inner edge of the Goldilocks zone. Even five percent closer to the sun, it is thought, and Earth too would look like Venus does today. If Earth was enough bigger than it is, it would have retained heat as if it were closer to the sun, and would not be habitable today. So if you're going to have a much bigger planet than Earth, push it a little further from its sun to be safe - or give it a slightly smaller sun.

No tectonics -
There are three forces that create mountains on Earth, the largest of which is tectonics. The two minor forces are impact cratering and volcanoes. Volcanoes are primarily driven by tectonics, so without tectonics there would likely be no active volcanoes today. Most impact craters in the solar system were created in the first billion years of its existence. Due to erosion, there are very few surviving craters on Earth's surface today. Impact craters survive on the Moon because erosive forces are slight and because its lack of tectonics does not recycle its crust.

There is an additional mountain forming process that is not seen on earth. Planets formed when lots of smaller bits fell to a common center. The heat of impact was not dissipated to space because other bits were piling on top and holding it in. Eventually the heat rose high enough the rocks melted. The earth's center is still molten with the heat of creation and of radioactive decay. That heat drives plate tectonics. The amount of heat originally produced is roughly proportional to the planet's volume. The amount it can radiate to space is a function of its surface area. Volume is proportional to the cube of a planet's radius but surface area is proportional to the square of its radius. This is a long-winded way of saying that bigger planets cool more slowly that smaller ones.

Because of faster cooling, smaller planets of the same age will have thicker crusts than larger ones. When the crust is thick enough, its mechanical strength becomes greater than the currents driving continental drift, and tectonics cease. But solid forms of a material are generally more compact than their liquid forms. (Water ice is a notable exception to this.) In a very small planet, a thick and rigid crust forms, but that's not the end of it. The molten interior continues to cool and to shrink. The crust, no longer supported, cracks and collapses inward, forming long scarps that run for thousands of kilometers.

So even without tectonics, you can still have mountains. On a planet with an atmosphere and especially with water, those mountains will be eroded away fairly quickly (geologically speaking). Continents may not disappear, but they would appear to our eyes flat and featureless. The weather patterns on such a world would be very different. Mountains form rain shadows, for example. Water-laden clouds can't get over the mountains. If they are pushed high enough to get over, they cool enough they drop most of their water as rain. When the Indian subcontinent slammed into Asia and raised the Himalayas, it change the world's weather patterns. I don't know enough to predict how weather would be different in a mountainless world, but we can be sure it would be very different.

Ice Age or Tropical Age -
We don't really know what causes an ice age. One theory that has pretty good traction is that the Earth's climate, a chaotic system (chaotic in the mathematical sense), has regions of relative stability. One of them is a warmer regime more or less like the historical norm, and another is an ice age regime. This theory is bolstered by the cyclic nature of ice ages. A 'tropical age', if there is such a thing, might be another stable regime.

Climate changes over time and we are far from having a complete understanding of it. But we do know that it's primarily a heat engine. The more heat that's in the atmosphere, the more active the climate is. People are often surprised at how close those climactic regimes are. Cool the Earth by 4.5 Kelvins and we'll have an ice age. Warm it by the same amount and the polar ice caps will be all gone. Warm it another 4.5 K and we'll have palm trees at the poles.

As to how well civilization would survive, that's an ongoing experiment. My guess is not too well. Our civilization is dependent on a small number of cereal crops. The best soil for growing those crops is found in the mid-latitudes of the northern hemisphere. Fortuitously, the temperatures at these latitudes are also suitable for these crops. If we shift the band of suitable temperature north or south by very much, which would be the case in an ice age or a tropical age, the best land for growing would no longer have a good climate for growing.

If the shift in climate occurred slowly enough, we might be able to develop new crops that could a) grow in the climate now found in mid-latitudes (but not if they're under ice), or b) grow well in the soils where the climate was now suitable. My guess, given how well we are currently cooperating on climate change, is that it would not happen without a major disruption.

There's another problem. Consider an ice age. Ice now comes down to, say, the forty-fifth parallel. How many people are displaced? Much of Europe is frozen, most of Russia, and the northern tier of states in the United States. Where will all those people go? Will they be welcomed with open arms? If they are accepted into southern countries will the ideas they bring be acceptable or disruptive? How will all those people be fed if the world's food supply is impacted?

Perhaps it's fortunate that the current experiment is with global warming and not global cooling.

Climactic distributions -
You have several topics lumped into this one. I'll start with the easiest to answer, the one about a desert planet with no plants. Even that one is really two questions. First, for much of its history, Earth was a desert planet. Life got along fine in the oceans and didn't venture out of the mother. But of course, there were plants, just not on land. If we define a plant as an organism that can capture sunlight and turn it into energy, and then postulate a planet with no plants, what would it look like? It would be dead. If the planet has plate tectonics, there might be bacterial life that metabolizes sulfur compounds near undersea vents, but that's about it. Without plants, there can be no animals. Animals get their energy from eating plants or from eating animals that eat plants.

Such a planet would not have an oxygen atmosphere. Oxygen is a highly reactive element. Free oxygen (O2) in the atmosphere is ephemeral. Sooner or later it will all react with something and pass out of the air. We have oxygen in the air because we have living beings (plants, mostly) that give off oxygen as a waste product and constantly replenish the oxygen that is lost. If we ever find a planet with free oxygen in the atmosphere, it will be a planet with life on it.

The climate of a location on Earth is determined firstly by water and latitude. The latitude determines how much solar energy you get and hence the temperature. Water determines if you're living in a desert or not. How much water you get depends on ocean currents and geography. Google climate zones and you'll see how they are distributed on Earth. Currents in the northern hemisphere move in clockwise gyres; they go counterclockwise in the southern hemisphere. Places with similar latitudes and similar relations to ocean currents have similar climates. Britain and the Pacific Northwest have climates with much in common. So do the eastern coast of North America and the coast of China. Southeast Asia and the Caribbean Basin are both prone to hurricanes and cyclones. The seaward side of mountain ranges is always wetter than the inland side.

The reason latitude is important is twofold. First, he further poleward you go, the lower the angle of the sun in the sky. A higher percentage of the light reaching Earth reflects off the atmosphere at higher latitudes and the light that reaches the ground is attenuated through more atmosphere. Second, axial tilt changes how great the seasonal changes are. In the tropics, seasonal changes are not very significant. In the polar regions, the difference between a winter with no sun and a summer with no night can be extreme.

Changing the axial tilt on your world will change how latitude interacts with climate. A lesser axial tilt will push the regions of negligible seasonal difference poleward but will not eliminate the other regions: they will be compressed instead. You'll still have a land (or sea) of the midnight sun, but it won't be as extensive. It will only disappear if your axial tilt is very small.

There is a lot more to climate than I've touched on, and a lot more than I'm qualified to speak to, so I'll stop while I'm ahead.

A topic you did not touch on is how the star around which your planet orbits will affect the planet, but perhaps that's a topic for another time.

How would work a world with a Huge big nebula visible in their sky ? Woudl have any effect like radiation , killing lifeforms or instead would have mostly no effect and allow the civilizations to rise?

Nested moons
Coudl a moon have a secondary moon orbiting it ? What consequences coudl be on the Earth?

Moon of a Larger Giant gas
Coudl a Earth develop under the influence of a giant Gas ? What coudl prevent Radiation to kill anything on the surface? what are the conditions to
support an Earthlike planed with a Big Saturn or Jupiter in the Night Sky?

Twin suns
How would work Earthlike planets with a double sun in the sky shining on civilizations? Woudl those rise ?

Twin Earths ...
Could perhaps two earths orbit one near the other and form a double minisystem with both supporting life?

Ring in the Sky
What could cause to have a Earthlike planet a Ring of detrites all around the planet just Like Saturn?

Btw on the

Large igneous province
I meant a huge land of Lava , not only some Volcanic activity in a region ... Its a pretty like a sea of Lava or a lava lake on
the open surface .

Axial Tilting periodical movements

Could be possible small Axial tilting movements that bring the axis of the Earth much more down during a period and
upper in others so changing drastically the Climate based on very small periods ( at least geologically ) like for example
every 10 years or every 50 years or even less? Would that affect much the flora and fauna of the regions ? Perhaps
adapted climatic plants? Or massive migrations?

A mount Olympus ( from Mars ) Volcano on Earth
would air be breatheable still on its top ? how woudl be even gravity?

Large Chasms
I think we all have seen a lot of Large Chasms in the soil on most fantasy maps , but are those actually possible in RL
and what woudl be their origin ? how massive they could be ?

Nebula proximity
yes, some nebula are visible from earth, so life is possible

Nested moons
Yes but it seems it's really rare. You need to meet different conditions

the smaller moon need to be in the inside the Hill sphere of the larger moon : Hill sphere - Wikipedia, the free encyclopedia
the smaller the second moon is, and the larger the larger moon is, the easier it is to make it fit in the sphere. The Hill sphere will be larger if it's far from the planet.

so the consequences are limited because the moon can't be too big or too close to Earth. To test more specific scenario you could try Universe sandbox, there is a free trial: Universe Sandbox

Moon of a Larger Giant gas
I don't know enough to answer

Twin suns
Yes if the second star is far enough. The closer it is, the hotter it becomes. Until the planet become a desert.
You can have 2 stars orbiting close to each other near the center of the system. The impact on the temperature could be small if you put the planet farther from them.
You can have the planet orbit 1 star and having a second star (smaller) orbiting around the main star but very far away. Or have the closest star orbit the other star is also possible.

Twin Earths ...
I don't know, they could become tidal locked to each other. Some parts of each planet would never have direct sunlight.

Ring in the Sky
having a moon that orbit too close to the planet. If the moon is small enough and if it's closing the distance slowly (and not crashing) it will disintegrate and create a ring. If the moon is too big, it could fall on the planet instead and killing pretty much everything.

You could also imagine a scenario in the future where the rings are made either of space junk or orbital infrastructures.

Large igneous province
Lava does not erupt in large quantity so it usually cools down pretty fast. That said, there was a time where earth was mostly made of lava. So it's possible but the planet could not host lifeforms without advanced technology.

Axial Tilting periodical movements
dunno
A mount Olympus ( from Mars ) Volcano on Earth
according to my knowledge some species could survive (in the lower stratosphere which is lower than the Olympus)but not humans. there is not enough oxygen.

Large Chasms
There is plenty of Chasms on Earth! The grand canyon and the rift in east Africa are some of the best examples. Usually, chasms get filled with water when they get big enough unless they form in the desert. The biggest one would be the Atlantic ocean.

One of the most well-known and easily visible nebulae in Earth's sky is the Orion nebula. It's about 1500 light years away from us. It's that little glowing smudge under Orion's belt.

But there are much larger nebulae out there in the universe. For instance, the LMC is a nearby dwarf galaxy visible in Earth's southern skies. It has a large nebula complex called the Tarantula nebula. The LMC is 180,000 light years away...yet the Tarantula nebula within it is still visible to the naked eye (the bright parts, anyway). This means that the Tarantula nebula is incredibly bright and titanically vast--it's one of the largest star-forming regions in our whole local group of galaxies.

Here's the kicker: if you were to take the Tarantula nebula and put it where the Orion nebula is, near Earth...it would FILL HALF THE NIGHT SKY. It would be so bright that it would cast shadows. Imagine looking up into the sky every night (for half the year, anyway) and seeing a vast, frozen inferno of filamentous glowing gasses. Yet it would still be more than a thousand light years from the planet, meaning that life would be relatively safe from radiation, supernovae, etc. (Relatively safe. If I were a god planning on making a home for life forms, I would probably not choose to locate their planet on the edge of an active star-forming region. If you want to make your planet safe for life in such a situation, just make sure it has a big, strong magnetic field and is orbiting a powerful sun capable of clearing a bow shock through those nebular outskirts.)

Moon of a Large Gas Giant
I think most physicists believe this to be entirely possible. A gas giant can get very large before it ignites to form a star. Some estimates are that it would take TEN Jupiter masses before nuclear fusion could ignite. So Jupiter is already huge, but you can get a lot bigger and still be a gas giant planet. A big gas giant can have very large moons: Ganymede is larger than Mercury or Pluto. Something the size of Mars or Earth could easily orbit a large gas giant.

As for radiation, the inhabitants of such a moon would be even better off than they are on Earth. Jupiter has a massive magnetic field that deflects a great deal of solar and interstellar radiation. And an earth-size moon could easily have its own strong magnetic field adding to that protection. Even Ganymede has its own magnetosphere.

As for warmth, it's true that Jupiter is quite a ways out in the solar system, and thus gets a tiny fraction of the solar radiation the Earth does. This means that Ganymede, Callisto, and Europa are all frozen solid on the surface. But we now know that jupiter-like gas giants don't need to be far from their star. Our planetary surveys have shown many "hot jupiters" orbiting nearby stars at many distances, from the baking zone of Mercury and Venus out to the goldilocks zone (liquid water) of Earth. It's entirely possible to have an inhabited gas giant moon at a comfortable range. Plus, the gas giant itself is likely radiating some heat. Jupiter does this: it puts out more heat into the universe than its taking in. We're not entirely sure why...we know it's not fusion going on, but must be some other process deep within the planet.

And while its true that Io is super hot due to jupiter's tidal forces heating it up, that wouldn't necessarily happen to any inhabited moon. It's all a function of the orbital distance.

Atmosphere is no problem for such a moon. Titan, for instance, has a very thick atmosphere with wind, rain, etc.